Zoom lens

Abstract

The invention relates to a zoom lens in which tweaks to the mode of movement of lens groups and the first lens group contribute more to making sure the desired zoom ratio and optical performances and ensuring that the whole length of the zoom lens is kept short while carrying it around. The zoom lens comprises a positive first lens group G1, a negative second lens group G2 and a positive third lens group G3, and includes an aperture stop S located between the second G2 and the third lens group G3. Upon zooming from the wide-angle end to the telephoto end, the first lens group G1 moves in unison, and the second lens group G2 moves in unison. The first G1 and the second lens group G2 are positioned nearer to the object side at the telephoto end than at the wide-angle end, with an increasing spacing between the first G1 and the second lens group G2 and a decreasing spacing between the second G2 and the third lens group G3. The zoom lens satisfies conditions (1) and (2) about the power and the amount of movement of the first lens group G1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is illustrative in section of Example 1 of the inventive zoom lens at the wide-angle end (a), in an intermediate state (b) and at the telephoto end (c), respectively.

FIG. 2 is illustrative, as in FIG. 1, of Example 2 of the inventive zoom lens.

FIG. 3 is illustrative, as in FIG. 1, of Example 2 of the inventive zoom lens.

FIG. 4 is illustrative, as in FIG. 1, of Example 2 of the inventive zoom lens.

FIG. 5 is illustrative, as in FIG. 1, of Example 2 of the inventive zoom lens.

FIG. 6 is an aberration diagram for Example 1 upon focusing on an object point at infinity.

FIG. 7 is an aberration diagram for Example 2 upon focusing on an object point at infinity.

FIG. 8 is an aberration diagram for Example 3 upon focusing on an object point at infinity.

FIG. 9 is an aberration diagram for Example 4 upon focusing on an object point at infinity.

FIG. 10 is an aberration diagram for Example 5 upon focusing on an object point at infinity.

FIG. 11 is a transverse aberration diagram for Example 1 upon focusing on an object point at infinity.

FIG. 12 is a transverse aberration diagram for Example 2 upon focusing on an object point at infinity.

FIG. 13 is a transverse aberration diagram for Example 3 upon focusing on an object point at infinity.

FIG. 14 is a transverse aberration diagram for Example 4 upon focusing on an object point at infinity.

FIG. 15 is a transverse aberration diagram for Example 5 upon focusing on an object point at infinity.

FIG. 16 is illustrative in section of a single-lens reflex camera with the inventive zoom lens used as an interchangeable lens.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Examples 1, 2, 3, 4 and 5 of the inventive zoom lens are now explained. FIGS. 1, 2, 3, 4 and 5 are illustrative in section of Examples 1, 2, 3, 4 and 5 at wide-angle ends (a), in intermediate states (b) and at the telephoto ends (c), respectively, upon focusing on an object point at infinity. Throughout the drawings, G1 stands for a first lens group, G2 a second lens group, S an aperture stop, G3 a third lens group, F various filters (low-pass filter, infrared cut filter, dustproof vibration filter, CCD cover glass, etc.) in the form of one single plane-parallel plate, and I an image plane (light receiving plane of an electronic imaging device).

EXAMPLE 1

As shown in FIG. 1, Example 1 is directed to a zoom lens made up of, in order from its object side, the first lens group G1 of positive refracting power, the second lens group G2 of negative refracting power, the aperture stop S, and the third lens group G3 of positive refracting power. Upon zooming from the wide-angle end to the telephoto end of the zoom lens, the first lens group G1 moves in unison toward the object side, and the second lens group G2 moves in a concave locus toward the object side with an increasing space between the first G1 and the second lens group G2 and is positioned nearer to the object side at the telephoto end than at the wide-angle end. The aperture stop S and the third lens group G3 move in unison toward the object side with a decreasing spacing between the aperture stop S and the second lens group G2.

In order from the object side, the first lens group G1 is made up of a cemented lens consisting of a double-convex positive lens and a negative meniscus lens concave on the object side; the second lens group G2 is made up of a negative meniscus lens convex on the object side, a cemented lens consisting of a double-concave negative lens and a positive meniscus lens convex on the object side and a negative meniscus lens convex on the image side; and the third lens group G3 is made up of a front subgroup composed of a double-convex positive lens and a cemented lens consisting of a double-convex positive lens and a negative meniscus lens concave on the image side and a rear subgroup composed of a positive meniscus lens convex on the image side, a double-convex positive lens and a negative meniscus lens convex on the image side.

Focusing from a distant object to a nearby object is implemented by moving the second lens group G2 toward the object side.

EXAMPLE 2

As shown in FIG. 2, Example 2 is directed to a zoom lens made up of, in order from its object side, the first lens group G1 of positive refracting power, the second lens group G2 of negative refracting power, the aperture stop S, and the third lens group G3 of positive refracting power. Upon zooming from the wide-angle end to the telephoto end of the zoom lens, the first lens group G1 moves in unison toward the object side, and the second lens group G2 moves in a concave locus toward the object side with an increasing space between the first G1 and the second lens group G2 and is positioned nearer to the object side at the telephoto end than at the wide-angle end. The aperture stop S and the third lens group G3 move in unison toward the object side with a decreasing spacing between the aperture stop S and the second lens group G2.

In order from the object side, the first lens group G1 is made up of a cemented lens consisting of a double-convex positive lens and a negative meniscus lens concave on the object side; the second lens group G2 is made up of a negative meniscus lens convex on the object side, a cemented lens consisting of a double-concave negative lens and a positive meniscus lens convex on the object side and a negative meniscus lens convex on the image side; and the third lens group G3 is made up of a front subgroup composed of a double-convex positive lens and a cemented lens consisting of a double-convex positive lens and a negative meniscus lens concave on the image side and a rear subgroup composed of a positive meniscus lens convex on the image side, a double-convex positive lens and a negative meniscus lens convex on the image side.

EXAMPLE 3

As shown in FIG. 3, Example 3 is directed to a zoom lens made up of, in order from its object side, the first lens group G1 of positive refracting power, the second lens group G2 of negative refracting power, the aperture stop S, and the third lens group G3 of positive refracting power. Upon zooming from the wide-angle end to the telephoto end of the zoom lens, the first lens group G1 moves in unison toward the object side, and the second lens group G2 moves in a concave locus toward the object side with an increasing space between the first G1 and the second lens group G2 and is positioned nearer to the object side at the telephoto end than at the wide-angle end. The aperture stop S and the third lens group G3 move in unison toward the object side with a decreasing spacing between the aperture stop S and the second lens group G2.

In order from the object side, the first lens group G1 is made up of a cemented lens consisting of a double-convex positive lens and a negative meniscus lens concave on the object side; the second lens group G2 is made up of a negative meniscus lens convex on the object side, a cemented lens consisting of a double-concave negative lens and a positive meniscus lens convex on the object side and a negative meniscus lens convex on the image side; and the third lens group G3 is made up of a front subgroup composed of a double-convex positive lens and a cemented lens consisting of a double-convex positive lens and a negative meniscus lens concave on the image side and a rear subgroup composed of a positive meniscus lens convex on the image side, a double-convex positive lens and a negative meniscus lens convex on the image side.

EXAMPLE 4

As shown in FIG. 4, Example 4 is directed to a zoom lens made up of, in order from its object side, the first lens group G1 of positive refracting power, the second lens group G2 of negative refracting power, the aperture stop S, and the third lens group G3 of positive refracting power. Upon zooming from the wide-angle end to the telephoto end of the zoom lens, the first lens group G1 moves in unison toward the object side, and the second lens group G2 moves in a concave locus toward the object side with an increasing space between the first G1 and the second lens group G2 and is positioned a little nearer to the object side at the telephoto end than at the wide-angle end. The aperture stop S move toward the object side with a decreasing spacing between the aperture stop S and the second lens group G2. The third lens group G3 moves toward the object side with a decreasing spacing between the aperture stop S and the third lens group G3.

In order from the object side, the first lens group G1 is made up of a double-convex positive lens and a double-concave negative lens; the second lens group G2 is made up of a negative meniscus lens convex on the object side, a cemented lens consisting of a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side and a double-concave negative lens; and the third lens group G3 is made up of a front subgroup composed of a double-convex positive lens and a cemented lens consisting of a double-convex positive lens and a negative meniscus lens concave on the image side and a rear subgroup composed of a double-convex positive lens, a positive meniscus lens convex on the object side and a double-concave negative lens.

EXAMPLE 5

As shown in FIG. 5, Example 5 is directed to a zoom lens made up of, in order from its object side, the first lens group G1 of positive refracting power, the second lens group G2 of negative refracting power, the aperture stop S, and the third lens group G3 of positive refracting power. Upon zooming from the wide-angle end to the telephoto end of the zoom lens, the first lens group G1 moves in unison toward the object side, and the second lens group G2 moves in a concave locus toward the object side with an increasing spacing between the first G1 and the second lens group G2 and is positioned a little nearer to the object side at the telephoto end than at the wide-angle end. The aperture stop S moves toward the object side with a decreasing spacing between the aperture stop S and the second lens group G2. The third lens group G3 moves toward the object side with a decreasing spacing between the aperture stop S and the third lens group G3.

In order from the object side, the first lens group G1 is made up of a double-convex positive lens and a double-concave negative lens; the second lens group G2 is made up of a negative meniscus lens convex on the object side, a cemented lens consisting of a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side and a double-concave negative lens; and the third lens group G3 is made up of a front subgroup composed of a double-convex positive lens and a cemented lens consisting of a double-convex positive lens and a negative meniscus lens concave on the image side and a rear subgroup composed of double-convex positive lens, a positive meniscus lens convex on the object side and a double-concave negative lens.

Numerical data in each of Examples 1 to 5 are set out. The symbols used hereinafter but not hereinbefore have the following meanings:

f: the focal length of the whole zoom lens system,

F is an F-number,

2ω is an angle of view,

WE is the wide-angle end,

ST is an intermediate state,

TE is the telephoto end,

r₁, r₂, . . . are the radii of curvature of the respective lens surfaces,

d₁, d₂, . . . are a spacing between the adjacent lens surface,

n_d1, n_d2, . . . are the d-line refractive indices of the respective lenses,

v_d1, v_d2, . . . are the Abbe number of the respective lenses, and

OD is a subject distance as measured from the image

EXAMPLE 1

r1 = 86.481	d1 = 4.99	nd1 = 1.6031	νd1 = 60.6
r2 = −108.395	d2 = 2.10	nd2 = 1.8467	νd2 = 23.8
r3 = −259.407	d3 = (Variable)
r4 = 35.302	d4 = 1.29	nd3 = 1.8052	νd3 = 25.4
r5 = 19.524	d5 = 4.38
r6 = −56.707	d6 = 1.01	nd4 = 1.5168	νd4 = 64.2
r7 = 20.158	d7 = 2.76	nd5 = 1.8467	νd5 = 23.8
r8 = 226.009	d8 = 1.27
r9 = −26.371	d9 = 1.00	nd6 = 1.7725	νd6 = 49.6
r10 = −229.620	d10 = (Variable)
r11 = ∞ (Stop)	d11 = 1.20
r12 = 69.845	d12 = 3.44	nd7 = 1.4875	νd7 = 70.2
r13 = −34.904	d13 = 0.15
r14 = 24.185	d14 = 4.99	nd8 = 1.4970	νd8 = 81.5
r15 = −24.185	d15 = 1.18	nd9 = 1.8010	νd9 = 35.0
r16 = −482.892	d16 = 13.90
r17 = −41.202	d17 = 2.01	nd10 = 1.5750	νd10 = 41.5
r18 = −22.237	d18 = 0.30
r19 = 97.144	d19 = 1.84	nd11 = 1.5168	νd11 = 64.2
r20 = −97.144	d20 = 6.83
r21 = −16.722	d21 = 0.94	nd12 = 1.7725	νd12 = 49.6
r22 = −40.266	d22 = (Variable)
r23 = ∞	d23 = 4.63	nd13 = 1.5163	νd13 = 64.1
r24 = ∞	d24 = 2.50
r25 = ∞(Imaging plane)
	WE	ST	TE
Zooming Data (OD = ∞)
	f (mm)	40.9	77.5	146.7
	FNO	4.1	4.8	5.8
	2ω (°)	30.5	16.4	8.7
	d3	2.31	37.66	48.35
	d10	17.47	10.74	2.10
	d22	28.43	33.81	54.53
(OD = 900 mm)
	d3	1.00	34.33	43.37
	d10	18.77	14.07	7.07
	d22	28.43	33.81	54.53

EXAMPLE 2

r1 = 86.036	d1 = 5.28	nd1 = 1.6031	νd1 = 60.6
r2 = −102.465	d2 = 2.10	nd2 = 1.8467	νd2 = 23.8
r3 = −248.790	d3 = (Variable)
r4 = 22.968	d4 = 1.09	nd3 = 1.8467	νd3 = 23.8
r5 = 16.162	d5 = 5.69
r6 = −53.640	d6 = 1.25	nd4 = 1.4875	νd4 = 70.2
r7 = 17.706	d7 = 2.55	nd5 = 1.8467	νd5 = 23.8
r8 = 71.411	d8 = 1.40
r9 = −29.601	d9 = 1.10	nd6 = 1.7725	νd6 = 49.6
r10 = −1996.707	d10 = (Variable)
r11 = ∞ (Stop)	d11 = 1.20
r12 = 56.884	d12 = 3.40	nd7 = 1.4970	νd7 = 81.5
r13 = −37.250	d13 = 0.15
r14 = 27.088	d14 = 4.81	nd8 = 1.4875	νd8 = 70.2
r15 = −22.581	d15 = 1.17	nd9 = 1.9037	νd9 = 31.3
r16 = −128.399	d16 = 12.75
r17 = −44.665	d17 = 2.09	nd10 = 1.5182	νd10 = 58.9
r18 = −23.113	d18 = 0.20
r19 = 485.119	d19 = 1.79	nd11 = 1.7618	νd11 = 26.5
r20 = −55.909	d20 = 8.44
r21 = −17.929	d21 = 0.88	nd12 = 1.9037	νd12 = 31.3
r22 = −42.416	d22 = (Variable)
r23 = ∞	d23 = 4.63	nd13 = 1.5163	νd13 = 64.1
r24 = ∞	d24 = 2.38
r25 = ∞(Imaging plane)
Zooming Data (OD = ∞)
		WE	ST	TE
	f (mm)	40.8	77.5	146.7
	FNO	4.1	4.8	5.8
	2ω (°)	30.6	16.4	8.7
	d3	2.34	35.87	46.81
	d10	17.36	10.50	2.10
	d22	28.68	34.69	55.22

EXAMPLE 3

r1 = 86.435	d1 = 4.99	nd1 = 1.6031	νd1 = 60.6
r2 = −108.218	d2 = 2.10	nd2 = 1.8467	νd2 = 23.8
r3 = −258.821	d3 = (Variable)
r4 = 35.358	d4 = 1.29	nd3 = 1.8052	νd3 = 25.4
r5 = 19.530	d5 = 4.36
r6 = −56.727	d6 = 1.01	nd4 = 1.5168	νd4 = 64.2
r7 = 20.161	d7 = 2.76	nd5 = 1.8467	νd5 = 23.8
r8 = 227.061	d8 = 1.27
r9 = −26.367	d9 = 1.00	nd6 = 1.7725	νd6 = 49.6
r10 = −231.956	d10 = (Variable)
r11 = ∞ (Stop)	d11 = 1.20
r12 = 69.809	d12 = 3.46	nd7 = 1.4875	νd7 = 70.2
r13 = −34.889	d13 = 0.15
r14 = 24.145	d14 = 5.02	nd8 = 1.4970	νd8 = 81.5
r15 = −24.145	d15 = 1.18	nd9 = 1.8010	νd9 = 35.0
r16 = −481.556	d16 = 13.78
r17 = −41.103	d17 = 2.08	nd10 = 1.5750	νd10 = 41.5
r18 = −22.222	d18 = 0.30
r19 = 97.372	d19 = 1.83	nd11 = 1.5168	νd11 = 64.2
r20 = −97.372	d20 = 6.85
r21 = −16.713	d21 = 0.94	nd12 = 1.7725	νd12 = 49.6
r22 = −40.204	d22 = (Variable)
r23 = ∞	d23 = 4.63	nd13 = 1.5163	νd13 = 64.1
r24 = ∞	d24 = 2.42
r25 = ∞(Imaging plane)
Zooming Data (OD = ∞)
		WE	ST	TB
	f (mm)	40.9	77.5	146.8
	FNO	4.1	4.8	5.8
	2ω (°)	30.5	16.4	8.7
	d3	2.30	37.54	48.16
	d10	17.45	10.72	2.10
	d22	28.60	34.03	54.94

EXAMPLE 4

r1 = 72.974	d1 = 3.42	nd1 = 1.6031	νd1 = 60.6
r2 = −221.186	d2 = 0.45
r3 = −363.380	d3 = 1.80	nd2 = 1.8052	νd2 = 25.4
r4 = 314.708	d4 = (Variable)
r5 = 105.397	d5 = 1.41	nd3 = 1.6712	νd3 = 57.6
r6 = 26.011	d6 = 3.92
r7 = 30.744	d7 = 0.98	nd4 = 1.5315	νd4 = 66.2
r8 = 16.748	d8 = 2.82	nd5 = 1.6869	νd5 = 30.2
r9 = 54.583	d9 = 1.48
r10 = −38.745	d10 = 1.06	nd6 = 1.7725	νd6 = 49.6
r11 = 136.360	d11 = (Variable)
r12 = ∞ (Stop)	d12 = (Variable)
r13 = 84.870	d13 = 2.33	nd7 = 1.4875	νd7 = 70.2
r14 = −47.027	d14 = 0.15
r15 = 23.439	d15 = 4.17	nd8 = 1.4970	νd8 = 81.5
r16 = −30.846	d16 = 1.14	nd9 = 1.9167	νd9 = 25.4
r17 = −204.810	d17 = 10.66
r18 = 167.137	d18 = 2.53	nd10 = 1.8628	νd10 = 21.9
r19 = −37.473	d19 = 0.28
r20 = 26.074	d20 = 2.40	nd11 = 1.6988	νd11 = 48.9
r21 = 110.272	d21 = 1.73
r22 = −35.799	d22 = 0.96	nd12 = 1.9037	νd12 = 31.3
r23 = 23.352	d23 = (Variable)
r24 = ∞	d24 = 4.63	nd13 = 1.5163	νd13 = 64.1
r25 = ∞	d25 = 2.42
r26 = ∞(Imaging plane)
Zooming Data (OD = ∞)
		WE	ST	TE
	f (mm)	40.8	77.5	147.9
	FNO	4.1	4.8	5.8
	2ω (°)	30.4	16.4	8.6
	d4	4.95	41.70	56.43
	d11	12.97	4.86	1.61
	d12	13.70	10.54	1.50
	d23	29.92	36.76	54.29

EXAMPLE 5

r1 = 61.767	d1 = 4.98	nd1 = 4.6031	νd1 = 60.6
r2 = −364.922	d2 = 0.43
r3 = −669.033	d3 = 1.80	nd2 = 1.8052	νd2 = 25.4
r4 = 218.268	d4 = (Variable)
r5 = 88.770	d5 = 1.40	nd3 = 1.6968	νd3 = 55.5
r6 = 21.437	d6 = 3.92
r7 = 28.845	d7 = 0.98	nd4 = 1.5168	νd4 = 64.2
r8 = 15.324	d8 = 3.12	nd5 = 1.6889	νd5 = 31.1
r9 = 54.554	d9 = 1.54
r10 = −36.674	d10 = 1.06	nd6 = 1.7725	νd6 = 49.6
r11 = 173.739	d11 = (Variable)
r12 = ∞ (Stop)	d12 = (Variable)
r13 = 67.230	d13 = 2.34	nd7 = 1.4875	νd7 = 70.2
r14 = −54.210	d14 = 0.15
r15 = 26.095	d15 = 4.14	nd8 = 1.4970	νd8 = 81.5
r16 = −31.627	d16 = 1.14	nd9 = 1.8467	νd9 = 23.8
r17 = −147.476	d17 = 12.63
r18 = 102.030	d18 = 2.30	nd10 = 1.8467	νd10 = 23.8
r19 = −42.159	d19 = 0.25
r20 = 28.758	d20 = 2.08	nd11 = 1.7015	νd11 = 41.2
r21 = 101.079	d21 = 1.72
r22 = −34.535	d22 = 0.96	nd12 = 1.9037	νd12 = 31.3
r23 = 27.307	d23 = (Variable)
r24 = ∞	d24 = 4.63	nd13 = 1.5163	νd13 = 64.1
r25 = ∞	d25 = 2.42
r26 = ∞(Imaging plane)
Zooming Data (OD = ∞)
		WE	ST	TE
	f (mm)	40.8	77.5	147.9
	FNO	4.1	4.8	5.6
	2ω (°)	30.4	16.4	8.6
	d4	3.60	43.92	54.41
	d11	13.10	4.12	1.48
	d12	11.22	10.85	1.50
	d23	29.60	34.19	53.33

FIGS. 6, 7, 8, 9, and 10 is an aberration diagram for Example 1, 2, 3, 4, and 5, respectively, upon focusing on an object point at infinity. In these aberration diagrams, (a), (b) and (c) are indicative of spherical aberration, astigmatism, distortion and chromatic aberration of magnification, respectively, at the wide-angle end, in the intermediate state, and at the telephoto end. FIGS. 11, 12, 13, 14, and 15 is a transverse aberration diagram for Example 1, 2, 3, 4, and 5 at the wide-angle end (a), in the intermediate state (b) and at the telephoto end (c), respectively, upon focusing on an object point at infinity. In FIGS. 11 to 15, ×0.4, ×0.7, ×0.9, and ×1.0 are indicative of the magnification of an image height with respect to the maximum image height, showing transverse aberrations at that image height.

Tabulated below are the values of conditions (1) to (12) in Examples 1 to 5.

		Exam-	Exam-	Exam-	Exam-
Conditions		ple 1	ple 2	ple 3	ple 4	Example 5
(1)	f1/ft	0.857	0.853	0.856	1.073	1.011
(2)	m1/ft	0.387	0.380	0.380	0.360	0.360
(3), (5)	Δn1	0.244	0.244	0.244	0.202	0.202
(4)	Δν1	36.8	36.8	36.8	35.2	35.2
(6)	m2/ft	0.073	0.077	0.075	0.005	0.016
(7)	m3	26.1	26.6	26.3	24.4	23.7
	1.5 × m2	16.1	17.1	16.5	1.2	3.6
	0.6 × m1	34.1	33.5	34.1	32.0	31.9
(8)	r2Gf/dt1	0.730	0.491	0.734	1.868	1.632
(9)	νpmax	81.500	81.500	81.500	81.500	81.500
(10)	νpmin	70.200	70.200	70.200	70.200	70.200
(11)	d3w/ft	0.095	0.087	0.094	0.072	0.085
(12)	ft/f3r	0.093	0.573	0.090	−0.514	−0.532

The aforesaid examples are each suitable for a zoom lens for single-lens reflex cameras that are used at a half angle of view of about 15° at the wide-angle end and on a relatively telephoto side as expressed by a zoom ratio of about 3 to 4.

In particular, each zoom lens is best suited for use with a single-lens reflex camera incorporating an electronic imaging device, because the associated camera can be made compact for carrying it around with improved performances by making the most of the ability of that to be downsized.

FIG. 16 is illustrative in section of a single-lens reflex camera in the form of an electronic imaging apparatus that makes use of the inventive zoom lens and employs a small-format CCD or CMOS as an imaging device. In FIG. 16, reference numeral 1 is indicative of a single-lens reflex camera; 2 of a taking system built in a lens barrel comprising a zoom mechanism and a focusing mechanism; and 3 of a lens barrel mount that makes the taking lens system attachable to or detachable from the single-lens reflex camera 1, for which a screw type mount or a bayonet type mount may be used. In the embodiment here, the bayonet type mount is used.

Reference numeral 4 is indicative of the plane of the imaging device; 5 of a quick return mirror located between a lens system and the plane 4 of the imaging device on an optical path 6 of the taking lens system 2; 7 of a finder screen located on a optical path taken by light reflected off the quick return mirror 5; 8 of a penta prism; 9 of a finder; and E of a viewer's eye (eye point).

The inventive zoom lens exemplified by Example 1, 2, 3, 4, and 5 may be used as the taking lens system 2 in the single-lens reflex camera 1 having such structure as mentioned above.

According to the invention as described above, it is possible to achieve a zoom lens that lends itself to an interchangeable lens suitable for use with a single-lens reflex type digital camera, and that works for making sure the desired zoom ratio and optical performances while the total length of the zoom lens is kept short.

Claims

1. A zoom lens comprising, from in order from an object side thereof, a first lens group having positive refracting power,a second lens group having negative refracting power anda third lens group having positive refracting power, wherein:there is an aperture stop located between said second lens group and said third lens group;upon zooming from a wide-angle end to a telephoto end of the zoom lens,said first lens group moves in unison, and said second lens group moves in unison, andsaid first lens group and said second lens group are positioned nearer to the object side at said telephoto end than said wide-angle end with an increasing spacing between said first lens group and said second lens group and a decreasing spacing between said second lens group and said third lens group; andsaid zoom lens is a three lens group type zoom lens that satisfies the following conditions (1) and (2): 0.7<f1/ft<1.2   (1)0.3<m1/ft<0.45   (2)

2. The zoom lens according to claim 1, which satisfies the following condition: 0.7<f1/ft<0.92   (1-1)

3. The zoom lens according to claim 1, wherein a combined system at the wide-angle end of said first lens group and said second lens group has negative refracting power.

4. The zoom lens according to claim 1, wherein: said first lens group is made up of two lenses, a negative lens and a positive lens, wherein a surface of said positive lens on a negative lens side is configured as a convex surface and a surface of said negative lens on a positive lens side is configured as a concave surface, and satisfies the following conditions (3) and (4): Δn1>0.05   (3)Δv1>20   (4)

5. The zoom lens according to claim 1, wherein: said first lens group comprises a cemented lens composed of a positive lens and negative lens in order from the object side, and satisfies the following condition (5): 0.05<Δn1<0.25   (5)

6. The zoom lens according to claim 1, which satisfies the following condition (6): 0<m2/ft<0.1   (6)

7. The zoom lens according to claim 1, wherein: upon zooming from the wide-angle end to the telephoto end, said third lens group moves in unison, and is positioned nearer to the object side at said telephoto end than at said wide-angle end.

8. The zoom lens according to claim 7, which satisfies the following condition (7): 1.5×m2<m3<0.6×m1   (7)

9. The zoom lens according to claim 1, wherein: said second lens group comprises, in order from the object side, a negative meniscus lens convex on an object side thereof, a cemented lens composed of a negative lens and a positive lens, and a negative lens.

10. The zoom lens according to claim 9, which satisfies the following condition (8): 0.3<r2Gf/dt1<2   (8)

11. The zoom lens according to claim 10, which satisfies the following condition (8-1): 0.5<r2Gf/dt1<1   (8-1)

12. The zoom lens according to claim 1, wherein: said third lens group comprises, in order from the object side, a front subgroup having positive refracting power and a rear subgroup having positive or negative refracting power, wherein:said front subgroup comprises two positive lenses and one negative lens, and satisfies the following conditions (9) and 10): 77<vpmax<90   (9)63<vpmix<80   (10)

13. The zoom lens according to claim 1, wherein: said third lens group comprises, in order from the object side, a front subgroup having positive refracting power and a rear subgroup having positive or negative refracting power, and satisfies the following conditions (11) and (12): 0.05<d3w/ft<0.2   (11)−0.7<ft/f3r<0.7   (12)

14. The zoom lens according to claim 13, which satisfies the following condition (12A): 0.1<|ft/f3r|  (12-A)

15. The zoom lens according to claim 13, which satisfies the following condition (12-1): 0<ft/f3r<0.13   (12-1)

16. The zoom lens according to claim 1, wherein focusing operation from a distant object to a nearby object is implemented by movement of said second lens group.

17. The zoom lens according to claim 1, which has a total angle of view of 25° to 35° at the wide-angle end and a zoom ratio of 3 to 5.